http://jsug.at/wiki/Meeting_49

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Jython
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Python on the JVM
Robert Bachmann
JSUG Meeting #49
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2. Outline
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Use Cases
Limitations
Usage & javax.script / JSR223
A (short) case study
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3. Python?
• Scripting language
• Dynamically typed
• Standard interpreter: (C)Python
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4. A broader view…
• JRuby (Ruby on the JVM)
• Groovy (native JVM language)
• CLR: IronPython & IronRuby
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5. Use cases
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Re-use of Java libraries
Re-use of Java infrastructure
Adding scripting abilities to a Java software
Prototyping
Test scripting
Performance improvements w.r.t (C)Python
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6. Limitations
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Not a Java replacement (cf. Scala)
No current compiler
Can not use Python modules with C code
Jython lags behind (C)Python & IronPython
Jython: 2.5.3 stable / 2.7a2 alpha
(C)Python: 2.7 stable
IronPython: 2.7 stable
• Performance worse than Java
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7. Usage
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“Hello World” with Jython
Using Java from Jython
Using Jython with javax.script
Using Jython from Java
Deployment options
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8. Hello World
# program.py
print ”Hello␣World”
$ jython program.py
Hello World
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9. Hello World with classes and modules
### demo.py
class Hello:
def greet(self, name):
print ”Hello␣” + name
### program.py
from demo import Hello
h = Hello()
h.greet(”JSUG”)
# or:
import demo
h = demo.Hello()
h.greet(”JSUG”)
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10. Using Java from Jython – Example
# Hello World with Swing
from javax.swing import JOptionPane
JOptionPane.showMessageDialog(None, ”Hello!”)
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11. Using Java from Jython – Notes
• Jython classes can
implement Java interfaces
extend Java classes
• Classpath
import uses classpath via sys.path
Add JARs via sys.path.append()
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12. javax.script
• JSR223: Scripting for the JavaTM Platform
• API for using scripting languages with Java
• Central class: ScriptEngine
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13. javax.script
ScriptEngineManager factory =
new ScriptEngineManager();
ScriptEngine engine =
factory.getEngineByName(”python”);
engine.eval(”print␣’Hello,␣World’”);
engine.put(”x”, 10)
engine.eval(”y␣=␣x␣*␣2”);
Object y = engine.get(”y”)
System.out.println(y)
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14. Using Jython classes from Java
• Steps:
Derive from Java class / interface
Use JythonInterperter to create an
instance
Call the instance’s __tojava__ method
• Complete solution:
http://www.jython.org/jythonbook/en/1.0/
JythonAndJavaIntegration.html
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15. Deployment options
• Servlet Contaier
org.python.util.PyServlet
WSGI via modjy
• Standalone .jar
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16. Case study
• Scenario: A C library with Java and .Net
wrappers
• Challenge: Automated testing of all libraries
• Solution: Single-source test automation
with Jython/IronPython
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17. Questions?
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18. Thanks
Twitter
@robertbachmann
Email rb@
—
.at
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